515691 divided by 51 
The aim is to understand the frequency of 51 in 515691.

On to step 1:
5 divided by 51 is 0 with a remainder of 5.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 5 and we're left with 5.
Append the next digit (1) from the dividend to 5 and continue with: 51 / 51

Advancing to step 2:
If we divide 51 by 51, we get 1 and a remainder of 0.
Write down 1 as next digit of the result. 
Result so far: 1.0
If we subtract 51 from 51, we get 0.
Grab the next digit (5) from the dividend, add it to 0, then carry on: 5 / 51

On to step 3:
The number 51 fits into 5 0 times, leaving a remainder of 5.
The number 0 becomes the next digit in our result. 
Result so far: 10.0
Deduct 0 from 5 and we're left with 5.
Bring next digit (6) of the dividend behind the 5 and repeat the process: 56 / 51

Let's proceed to step 4:
If we divide 56 by 51, we get 1 and a remainder of 5.
Record the quotient 1 as the next digit in the result. 
Result so far: 101.0
If we take 51 away from 56, we end up with 5.
Fetch the next digit (9) from the dividend, attach it to 5 and continue: 59 / 51

Step 5:
If we divide 59 by 51, we get 1 and a remainder of 8.
Write down 1 as next digit of the result. 
Result so far: 1011.0
If we subtract 51 from 59, we get 8.
Fetch the next digit (1) from the dividend, attach it to 8 and continue: 81 / 51

Going ahead to step 6:
When dividing 81 by 51, we get 1 with a remainder of 30.
Put 1 as the next digit of the answer. 
Result so far: 10111.0
If we subtract 51 from 81, we get 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

Moving on to step 7:
300 divided by 51 is 5 with a remainder of 45.
The number 5 becomes the next digit in our result. 
Result so far: 10111.5
If we subtract 255 from 300, we get 45.
Since there are no more digits in the dividend, we add a zero to the remainder making it 450, and continue the process.

On to step 8:
51 goes into 450 8 times with a remainder of 42.
Use 8 as the next digit of our solution. 
Result so far: 10111.58
Subtract 408 from 450 to get 42.
Since there are no more digits in the dividend, we add a zero to the remainder making it 420, and continue the process.

On to step 9:
51 can be fit into 420 8 times, resulting in a remainder of 12.
Put 8 as the next digit of the answer. 
Result so far: 10111.588
Subtract 408 from 420 to get 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

The quotient of the division is 10111.588, and the remainder is 0.0012.